1. Field of the Invention
The present invention relates to a shrink film package having a tape-shaped opening and method for making thereof.
2. Description of the Prior Art
In the past, heat-shrinkable film has been widely utilized in the packaging of many individual packages or bulk packages in units for distribution or transportation. However, the unpacking operation of such packages has been difficult due to the packaging film itself being hermetically confined over the outer surface of the product by the shrinking effect. To improve the unpacking operation, the following examples of measures have been taken, with reference to FIGS. 26-32, namely:
(1) Slits 101 are previously provided on the shrinkable film of the package 100 at the opening side thereof (FIG. 26). PA1 (2) Sealing portions of the packaging film are overlaid and adhered together, providing a reinforced grasping portion to be utilized as a tear-off tab 102 (FIG. 27). PA1 (3) After or before the shrinking treatment of the film, tear off slit 103 or 104 is provided to the sealing portion of the packaging film (FIGS. 28 and 29). PA1 (4) On the sealing portion of the packaging film, a reinforced article having higher strength than said film (such as string and tape) 105 is overlaid and adhered thereto (FIG. 30). PA1 (5) As disclosed in the Japanese Laid Open Patent 55-163128, after the shrinking treatment of the film, perforation 107 is provided in the center of the entire side surfaces of the package using a knife roll 106 (FIG. 31). PA1 (6) After the shrinking treatment of the film, perforations 108 are provided around the entire package traversing the sides thereof (FIG. 32).
Conventionally, in order to have easy opening of the shrink film package, the above measures have been taken and it is also known, similarly to (4) above, that: a separate heat-shrinkable tearing tape other than packaging film is welded to the packaging film at the time of the shrinking process of the shrink film package (Japanese Laid Open Utility Model 55-86758); or a plastic tape or paper tape of different material than the packaging film is incorporated into the opening portion of the package to easily break off therefrom through the tape (Japanese Patent Publication 59-408). All of these measures have inconveniences as hereinafter mentioned which reduce their commercial value.
The problems are that according to the method of (1) aforementioned, the strength of the package is not only decreased due to the slit in the packaging film thereto, but also a slit does not always work to tear off the film, depending on the film used. According to the method of (2) aforementioned, since the breaking point is harder than the base film because of the reinforcement, tearing off the film is so difficult that the working efficiency of the opening is worse than the method of (1). Also, the opening is not regular which causes the further problem that the break in the surface of the film is jagged with an unattractive appearance. According to the method of (3) aforementioned, there are the disadvantages of providing a complicated device to make the slit and the slit decreases the entire package strength. According to the method of (4), the different nature of the reinforced article adhered to the packaging film increases the difficulty of tearing off, and further, the different materials of the reinforced article and the packaging film has the disadvantage that the appearance of the package after the shrinking treatment becomes less desirable. And the method according to (5) above creates the problem that it is dangerous to scratch the package so that the applications are limited to hard surface and flat-shaped packages, and also the perforations expand and the film breaks while shrinking is done, and thus the package strength is decreased.
While polyethylene film has been generally used for shrinkable film for middle or heavy weight packages, or for large size of bulk packing, it is difficult to unpack the package because the film is flexible and expandable so that the tear-off opening is not able to break off cleanly along a line of perforations. In addition , when the shrink package is made by a sheet of perforated polyethylene film, hot-air-blowing temperature in the shrink tunnel is set near the temperature of the melting point of polyethylene, and thereby the perforations are entirely welded and expanded, causing breaking of the film.